ID: XX-XXXX; -19-0016 1 1 T D Le Cras and E Boscolo PIK3CA-related vascular 1:1 H33–H40 anomalies MINI REVIEW Cellular and molecular mechanisms of PIK3CA-related vascular anomalies Timothy D Le Cras1 and Elisa Boscolo2 1Division of Pulmonary Biology, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati Children’s Hospital, Cincinnati, Ohio, USA 2Experimental Hematology and Cancer Biology, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati Children’s Hospital, Cincinnati, Ohio, USA Correspondence should be addressed to E Boscolo: [email protected] Abstract The phosphoinositide 3-kinase (PI3K) pathway is a major mediator of growth factor Key Words signaling, cell proliferation and metabolism. Somatic gain-of-function mutations in PIK3CA, f vascular malformation the catalytic subunit of PI3K, have recently been discovered in a number of vascular f vascular anomalies anomalies. The timing and origin of these mutations remain unclear although they are believed to occur during embryogenesis. The cellular origin of these lesions likely involves endothelial cells or an early endothelial cell lineage. This review will cover the diseases and syndromes associated with PIK3CA mutations and discuss the cellular origin, pathways and mechanisms. Activating PIK3CA ‘hot spot’ mutations have long been associated with a multitude of cancers allowing the development of targeted pharmacological inhibitors that are FDA-approved or in clinical trials. Current and future therapeutic approaches for PIK3CA-related vascular anomalies are discussed. The phosphoinositide 3-kinase pathway The phosphoinositide 3-kinase (PI3K) signaling pathway (α-helical domain), and p.H1047R/L (H, histidine replaced is a critical regulator of the angiogenic process by by R, arginine or L, leucine at amino acid position 1047) controlling endothelial cell (EC) proliferation, migration in exon 20 (kinase domain) are common in cancer (6), and survival (1). Growth factor stimulation of receptor and more recently, have also been identified in pediatric tyrosine kinases activates PI3K that in turn catalyzes the vascular anomalies and overgrowth syndromes. All of the conversion of phosphatidylinositol (3,4)‐bisphosphate PIK3CA mutations associated with vascular anomalies (PIP2) to phosphatidylinositol (3,4,5)‐triphosphate (PIP3). and cancer are non-inherited and lead to sequestration PIP3 triggers phosphorylation of Pyruvate Dehydrogenase of the p110α subunit to the plasma membrane thereby Kinase 1 (PDK1), which phosphorylates the serine and generating constitutive hyper-activation of the PI3K‐AKT threonine kinase AKT (also known as Protein Kinase B, pathway (7). Of interest, sustained AKT activation PKB) (2, 3). This activation of AKT leads to increased induces pathological angiogenesis and increased blood cellular proliferation through the mTOR pathway (4, 5). vessel diameter (8). Germline transmission of the PIK3CA The catalytic subunit of PI3K (p110α) is encoded by the oncogenic ‘hotspot’ mutations is not compatible with PIK3CA gene. PIK3CA ‘hot spot’ mutations p.E542K (E, life. In mouse, ubiquitous or Tie2-driven heterozygous glutamic acid replaced by K, lysine at amino acid position expression of Pik3ca H1047R resulted in disrupted vascular 542) and p.E545K (amino acid position 545) in exon 9 remodeling in the embryonic and extraembryonic tissues https://vb.bioscientifica.com © 2019 The authors This work is licensed under a Creative Commons https://doi.org/10.1530/VB-19-0016 Published by Bioscientifica Ltd Attribution-NonCommercial-NoDerivatives 4.0 International License. Downloaded from Bioscientifica.com at 09/24/2021 06:28:57PM via free access T D Le Cras and E Boscolo PIK3CA-related vascular 1:1 H34 anomalies Q1 and lethality prior to E11.5 (9). Conversely, ubiquitous (17). Somatic activating PIK3CA mutations have been expression of Pik3ca H1047R in 6–8-week-old mice caused identified in affected tissue resected from the majority increased body weight, organomegaly and metabolic (94%) of LM patients (18) and in cells isolated from LM defects (10). tissue (19, 20, 21). Patient-derived lymphatic endothelial cells (LM-LEC) exhibit pro-angiogenic properties such as increased proliferation, sprout formation, and VEGF-C PIK3CA mutations in vascular anomalies and VEGFR-3 overexpression. AKT that is downstream of PI3K is constitutively active in the mutant LM-LEC, While vascular malformations are primarily present at while ERK1/2 phosphorylation levels are variable birth, they can also become apparent during childhood, (17, 19, 20, 22). A few animal models of LM have and they persist throughout adulthood. The International been reported and consist of xenografts generated by Society for the Study of Vascular Anomalies (ISSVA) injection of LM-LEC (17) or LEC progenitor cells (23). In created a classification system to aid the diagnosis of these these studies, it is unclear if implanted cells expressed anomalies (11). A number of genes and gene mutations PIK3CA mutations. Another model of thoracic LM have been implicated with vascular anomalies, in this was generated by overexpression of VEGF-C in mouse review we will focus on the disease categories associated airway epithelial cells resulting in lymphangectasia and with PIK3CA mutations (Table 1). mTOR pathway activation (24), although the specific activation status of AKT was not assessed. In the future, improved PIK3CA-based models of LM would be very Simple vascular anomalies beneficial to investigate therapeutic targets. Lymphatic malformations (LM) Generalized lymphatic anomaly (GLA) Lymphatic malformations (LM) are characterized by massively dilated and dysmorphic low-flow lymphatic Generalized lymphatic anomaly (GLA) is a severe form of channels (12, 13, 14, 15, 16) lined with flattened LM that is diffuse or multifocal. Patients have increased EC. Often, vessels are filled with blood or thrombi risk of pulmonary involvement and the dysmorphic as result of intralesional trauma and/or improper lymphatics can infiltrate and compromise the medullary communication with the venous system. Expansion bone causing pain and compromised mobility (25, 26). of LM is caused by vascular distension generated A high-throughput sequencing effort led to the discovery by fluid accumulation and cellular hyperplasia. LM of PIK3CA mutations in affected tissue and LEC in 55% expands during adolescence, and lesions can cause of GLA patients (27). Postnatal transgenic expression severe disfigurement, affect vital organs and contribute of PIK3CA p.H1047R in the LEC (Prox1-CreERT2) caused to infections. Histological markers of LM are Prox-1 lymphatic hyperplasia and dysfunction, modeling and VEGFR3, while Podoplanin levels can be variable important aspects of GLA (27). Table 1 Genetic mutations in vascular anomalies. Vascular anomalies Gene mutations References Vascular tumors KRAS, NRAS, HRAS, BRAF, GNAQ, GNA11, GNA14 (72, 73, 74, 75) Vascular malformations Simple Capillary malformation GNAQ, GNA11, KRAS (76, 77, 78) Lymphatic malformation PIK3CA (18, 19, 20, 21) Venous malformation TEK, PIK3CA (29, 31, 32, 33, 34, 35) Arteriovenous malformation KRAS, MAP2K1, BRAF (76, 79, 80) Combined Lymphatic-Venous malformation PIK3CA (81) Capillary-Lymphatic-Venous malformation/KTS, CLOVES PIK3CA (18, 46, 47, 48, 49) Capillary malformation-ArterioVenous malformation RASA1, EPHB4 (82, 83) Others Fibro-adipose vascular anomaly PIK3CA (18) Megalencephaly-capillary malformation PIK3CA (53) https://vb.bioscientifica.com © 2019 The authors This work is licensed under a Creative Commons https://doi.org/10.1530/VB-19-0016 Published by Bioscientifica Ltd Attribution-NonCommercial-NoDerivatives 4.0 International License. Downloaded from Bioscientifica.com at 09/24/2021 06:28:57PM via free access T D Le Cras and E Boscolo PIK3CA-related vascular 1:1 H35 anomalies Q1 Venous malformation (VM) PIK3CA-Related Overgrowth Syndromes (PROS) (40). CLOVES syndrome is characterized by a combination of Venous malformation (VM) manifests as unifocal or vascular, skin, lipomatous overgrowth and musculoskeletal multifocal bluish compressible lesions and may affect abnormalities (45). PIK3CA somatic mutations have been any tissue or organ. Patients with VM can suffer severe identified in a high percentage (~90%) of KTS and CLOVES disfigurement, painful swelling, chronic recurrent thrombi patients (18, 46, 47, 48). An interesting distinctive feature and increased risk for pulmonary thromboembolism of KTS is that the PIK3CA variant p.C420R, relatively (13, 28). The histological hallmarks of VM are slow-flow frequent in CLOVES, has not been reported in KTS patients thin-walled ectatic veins with scant smooth muscle cells. (18, 46, 48, 49). A postnatal murine model of CLOVES Pioneering work by Miikka Vikkula’s group identified was recently generated through ubiquitous expression of germline or sporadic somatic activating TIE2 (TEK) a dominant active PIK3CA transgene (P110*) (50, 51, 52). mutations in about 60% of VM cases (29, 30, 31, 32). More recently, three independent studies described PIK3CA mutations in about 25% of VM patients (33, 34, 35). PIK3CA mutations are more frequent in intramuscular Other vascular anomalies VM that do not involve the skin (35). TIE2 and PIK3CA A range of overgrowth syndromes combined with vascular mutations are typically mutually exclusive but in few anomalies have been associated with PI3KCA mutations. patients both occurred (33, 34, 35, 36). The result of Fibro-adipose vascular anomaly